Search

The NEMO-3 experiment at the Modane Underground Laboratory has investigated the double-$\beta$ decay of $^{48}{\rm Ca}$. Using $5.25$ yr of data recorded with a $6.99\,{\rm g}$ sample of $^{48}{\rm Ca}$, approximately $150$ double-$\beta$ decay candidate events have been selected with a signal-to-background ratio greater than $3$. The half-life for the two-neutrino double-$\beta$ decay of $^{48}{\rm Ca}$ has been measured to be $T^{2\nu}_{1/2}\,=\,[6.4\, ^{+0.7}_{-0.6}{\rm (stat.)} \, ^{+1.2}_{-0.9}{\rm (syst.)}] \times 10^{19}\,{\rm yr}$. A search for neutrinoless double-$\beta$ decay of $^{48}{\rm Ca}$ yields a null result and a corresponding lower limit on the half-life is found to be $T^{0\nu}_{1/2} > 2.0 \times 10^{22}\,{\rm yr}$ at $90\%$ confidence level, translating into an upper limit on the effective Majorana neutrino mass of $ < 6.0 - 26$ ${\rm eV}$, with the range reflecting different nuclear matrix element calculations. Limits are also set on models involving Majoron emission and right-handed currents.

The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double $\beta$ ($0\nu\beta\beta$) decay. We report final results of a search for $0\nu\beta\beta$ decays with $6.914$ kg of $^{100}$Mo using the entire NEMO-3 data set with a detector live time of $4.96$ yr, which corresponds to an exposure of 34.3 kg$\cdot$yr. We perform a detailed study of the expected background in the $0\nu\beta\beta$ signal region and find no evidence of $0\nu\beta\beta$ decays in the data. The level of observed background in the $0\nu\beta\beta$ signal region $[2.8-3.2]$ MeV is $0.44 \pm 0.13$ counts/yr/kg, and no events are observed in the interval $[3.2-10]$ MeV. We therefore derive a lower limit on the half-life of $0\nu\beta\beta$ decays in $^{100}$Mo of $T_{1/2}(0\nu\beta\beta)> 1.1 \times 10^{24}$ yr at the $90\%$ Confidence Level, under the hypothesis of light Majorana neutrino exchange. Depending on the model used for calculating nuclear matrix elements, the limit for the effective Majorana neutrino mass lies in the range $\langle m_{\nu} \rangle < 0.33$--$0.62$ eV. We also report constraints on other lepton-number violating mechanisms for $0\nu\beta\beta$ decays.

This Letter reports results from the NEMO-3 experiment based on an exposure of 1275 days with 661g of 130Te in the form of enriched and natural tellurium foils. With this data set the double beta decay rate of 130Te is found to be non-zero with a significance of 7.7 standard deviations and the half-life is measured to be T1/2 = (7.0 +/- 0.9(stat) +/- 1.1(syst)) x 10^{20} yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.

No evidence for the neutrinoless double-\ensuremath{\beta} decay of $^{100}\mathrm{Mo}$ has been found in a search using a segmented Si(Li) detector with source foils enriched to 97% $^{100}\mathrm{Mo}$. After 0.2664 mole years of exposure, we report a 1\ensuremath{\sigma} lower limit on the half-life for the ${\mathit{J}}^{\mathit{P}}$=${0}^{+}$\ensuremath{\rightarrow}${0}^{+}$ transition of 0.44\ifmmode\times\else\texttimes\fi{}${10}^{23}$ years.

The high-spin states of /sup 78/Kr have been studied through observation of ..gamma.. rays emitted from the /sup 68/Zn(/sup 12/C,2n) reaction produced with projectile energies of 33--38 MeV. The energies, relative intensities, angular distributions, and linear polarizations of the ..gamma.. rays were measured. Lifetimes of states were obtained from the Doppler broadening of the ..gamma..-ray peaks. Many of the levels appear to belong to one of three bands: (1) the ground-state band with energy spacing between that given by the pure rotational and vibrational models, (2) a band built on a 5/sup -/ state which is ascribed to rotational alignment of two quasiparticles, one of which is in a g/sub 9/2/ orbital, and (3) a ..delta..J=1 band which has characteristics of a ..gamma..-vibrational band in a deformed nucleus. There is evidence for the beginning of a fourth band built on a J=6 level.

Measurements of the absolute neutron yield and the time dependence of the appearance of neutrons resulting from muon-catalyzed fusion have been carried out in high-density deuterium-tritium mixtures. The temperature dependence of the resonant dt..mu..-molecular formation process has been determined in the range 100 to 540 K. Mesomolecular formation is found to be resonant for DT as well as D/sub 2/ target molecules. The sticking probability and other fundamental parameters have been measured for the first time.

Low- and high-spin states of /sup 68/Ge are investigated through in-beam ..gamma..-ray spectroscopy via the /sup 58/Ni(/sup 12/C,2p), /sup 63/Cu(/sup 7/Li,2n), and /sup 52/Cr(/sup 19/F,p2n) reactions. A surprising richness of collective bands is observed in /sup 68/Ge including three even parity bands built on 8/sup +/ levels, the lower two of which are assigned as rotational aligned bands built on both proton and neutron (g/sub 9/2/)/sup 2/ configurations, and three odd parity bands built on ..pi.. and ..nu.. configurations that include the g/sub 9/2/ orbit. Details of the multiple bands and other levels observed in /sup 68/Ge are presented. Rotation-aligned model calculations and interacting boson model calculations for /sup 68/Ge are also described.

The linear polarizations of /sup 64/Zn ..gamma.. rays, produced in the /sup 59/Co(/sup 7/Li,2n) reaction with E/sub 7Li/ = 18 MeV, have been measured with a Ge(Li) two-crystal Compton polarimeter. These polarization values were used with previously obtained ..gamma..-ray angular distribution measurements to make unique parity assignments for several states. The 641- and 1619-keV ..gamma.. rays have been found to be predominantly E1 transitions, and odd parity has been assigned to the levels at 2999 keV (3/sup -/), 3925 keV (5/sup -/), 4635 keV (7/sup -/), 4981 keV (7/sup -/), and 5681 keV (8/sup -/). Even parity assignments have been confirmed for levels at 991 keV (2/sup +/), 2736 keV (4/sup +/), 3994 keV (6/sup +/), and 4237 keV (6/sup +/). Also, the spin assignments for levels at 2307 keV (4/sup +/) and 4635 keV (7/sup -/) have been confirmed.

The pionic x-ray energies of the $4f\ensuremath{-}3d$ transition in $\ensuremath{\pi}$-P and the $5f\ensuremath{-}4d$ transition in $\ensuremath{\pi}$-Ti were measured with a bent-crystal spectrometer at the Nevis synchrocyclotron; and a new value of the pionic mass is deduced to be 139 567.5\ifmmode\pm\else\textpm\fi{}0.9 keV, leading to an improved value for the $\ensuremath{\mu}$-neutrino mass of ${{m}_{{\ensuremath{\nu}}_{\ensuremath{\mu}}}}^{2}$=0.102\ifmmode\pm\else\textpm\fi{}0.119 ${\mathrm{MeV}}^{2}$; ${m}_{{\ensuremath{\nu}}_{\ensuremath{\mu}}}l0.52$ MeV, at 90% confidence level.

A newly designed, large-aperture and high-resolution bent-crystal spectrometer has been used to observe high-intensity sources of pionic x rays. The pionic x-ray source was a target of natural titanium which was placed adjacent to a copper pion-production target in the external beam of the Nevis synchrocyclotron. The energy difference between the 5g ..-->.. 4f and 5f ..-->.. 4d transitions in pionic titanium was measured to be 87.6 +- 1.8 eV. Comparison with the prediction of the Klein-Gordon equation is made.

We report the results of an experimental search for neutrinoless double-{beta} decay using isotopically enriched foils of {sup 100}Mo interleaved in a stack of 40 silicon detectors. With an exposure of 69.9 mole days, we place lower half-life limits on the {ital J}{sup {ital P}}=0{sup +}{r arrow}0{sup +} transition of 4{times}10{sup 21} yr (68% C.L.) and on the 0{sup +}{r arrow}2{sup +} transition of 4{times}10{sup 20} yr (68% C.L.).